When the loyalty of a NPC is too high, you need more points to open the option of suggest anything. You can lower it down by doing 'romantic options' (flirt, wink, etc). It will slowly lower down NPC's loyalty (if it is in a relationship).One important detail, Only sucessfull interactions will lower down the loyalty. After a lot of flirty, winks and pick up lines, once in a while you can try to hug (more points for cheat) and kiss (harder than hug but have better results).
This one looks like one really loyal. It really is hard. There is a list of things you will need to do.
1- Flirt, wink and pick up lines. Mixed with other interactions, so she dosen't reject you for repetitive actions.
2- Once she accept hugs, insert hugs in the sequence of interactions.
3- Once she starts to accept suggestions for cheat, do it... If you want you can suggest other things you like as well to make sure she will behave the way you want on sex (and gain more points).
4- Once she starts to accept kisses, do it!
5- Keep going until she say yes for sex.
This process can take a long time if she really is loyal (as it should be).
Good good?
If you have any doubt just comment here and i'll try to help you!